CBCT-Guided Online Adaptive Radiotherapy for Isotoxic Dose Escalation In Hypofractionated Treatment of Locally Advanced Lung Cancer
Abstract
Purpose
While hypofractionation and dose escalation may provide enhanced tumor control in locally advanced lung cancer, previous attempts generally increase toxicity (e.g., esophagitis and/or pneumonitis). We present an approach leveraging CBCT-guided online adaptive radiotherapy(oART) to ensure that daily plans maximize target dose while respecting organ-at-risk(OAR) tolerances in the face of anatomical variability.
Methods
Stage III NSCLC patients(n=12) treated with CBCT-guided oART in 15 fractions (180 total oART treatments) were analyzed. Target accounting for internal respiratory motion(IGTV) from 4DCT simulation was rigidly propagated/aligned daily to maintain the 300cGy/fraction dose cloud. Critical OARs (e.g., proximal bronchial tree(PBT), esophagus) were re-contoured on daily CBCT to derive daily region to safely receive dose escalation (400cGy/fraction). Daily OAR sparing and target coverage for scheduled(SCH) versus adapted(ADP) plans were evaluated. Manual IGTV-guided rigid registration of daily dose distributions provided cumulative dose estimation to examine the benefit of daily hotspot migration with oART.
Results
Average oART session time (CBCT acquisition to treatment completion) was 31.2±6.9 minutes. Daily adaptation improved PBT sparing by an average 7.9% (average D0.03cc of 359cGy (range:327-372) versus 392cGy (range:331-466) for ADP versus SCH, respectively; Goal: D0.03cc<369cGy/fraction). Even with improved OAR sparing, IGTV coverage remained comparable, with average daily V400cGy favoring ADP over SCH by 3.0±13.9%. Cumulative dose highlighted decreased heterogeneity due to hotspot migration in ADP vs. SCH and also found that D0.03cc for PBT+5mm (margin accounting for registration uncertainty) decreased by 1.4%.
Conclusion
Daily oART for treatment of locally advanced lung cancer facilitates consistent target coverage at standard dose(300cGy/fraction) with additional isotoxic dose escalation(400cGy/fraction) to a dynamic portion of the target, defined to ensure OAR dosimetric tolerances are not violated. Analysis of daily dose demonstrates appreciable OAR dose reduction and comparable target coverage with adaptation. Cumulative dose assessment reveals improved target homogeneity as a result of hot-spot location varying daily with oART.